Conventionally known is a porous sheet provided with a porous base material including a polyolefin and a heat-resistant porous layer laminated on one surface or both surfaces of the porous base material by using a heat-resistant resin (for example, see Patent Document 1 and 2).
Patent Document 1 and 2 disclose non-aqueous secondary battery separators, in which a surface of a polyethylene microporous film has been coated with a heat-resistant porous layer composed of a heat-resistant polymer such as a wholly aromatic polyamide. In such separators, the polyethylene microporous film allows pores to close under high temperature. Thus, the separators have a function for blocking electric current to prevent thermal runaway of battery (shutdown function). Furthermore, in the separators, even if the polyethylene microporous film has been molten under high temperature conditions, the heat-resistant porous layer retains the shape thereof, which therefore can prevent short circuit between electrodes, thereby preventing accidents, such as thermal runaway and ignition of battery. In addition, a non-aqueous secondary battery having higher safety under high temperature can be provided.
Such a layered-type separator is used for layered-type batteries having a more flexible shape for use in mobile devices and the like and large-volume and large-size batteries for hybrid cars and the like.
From the viewpoint of the shape flexibility and increase in size, preferred is, for example, a layered-type battery, such as a layered-type battery in which a layered body including plural electrodes and separators laminated on each other has been wrapped in laminate packaging. However, in a battery having such as a laminate structure, due to an impact from outside the battery or the like can cause a shift between the electrodes and the separators, leading to the occurrence of short circuit. In view of such a concern, a layered-type battery is conventionally known in which electrodes individually have been housed in a separator formed into a pouch shape by folding the separator and bonding the ends thereof together by thermal fusion or the like to restrain movement of the electrodes (for example, see Patent Document 3).
Meanwhile, in ordinary production of battery, long and large electrode sheets and a separator are simultaneously sequentially conveyed and laminated to produce a battery element. In this case, for example, when a short separator is used, it is necessary to take measures, such as temporality stopping a production line in order to switch to a new separator in a short period of time or reducing the lengths of the electrode sheets to correspond to the length of the separator. Such measures lead to reduction in production efficiency of battery. In the situation as above, a method is thought to be effective, in which while continuing to operate the production line, the tip end of a new porous sheet is connected to the rear end of the porous sheet being conveyed, so that production line suspension is prevented. This method is preferable in that if the connecting can be accomplished by thermal fusion, processing is easy and simple.